The invention relates to a controllable or regulatable hydraulic shock absorber and, more particularly, to a controllable or regulatable hydraulic shock absorber having two working chambers The two working chambers are divided off from one another by a piston or a displacer. The two working chambers are connected to one another, for the exchange of hydraulic medium during stroke movements of the piston or displacer, via a damping-control valve arrangement. The damping-control valve arrangement includes a closing member stressed into the closing position by a spring arrangement which opens an orifice cross-section which depends on the pressure difference between the working chambers and on the force of an electromagnet arrangement controlling the closing member and having an armature arrangement located between the closing member and the spring arrangement.
At the same time, the electromagnet arrangement is preferably designed as a proportional magnet, so that the adjusting force essentially depends only on the intensity of the electrical current passing through the magnet. Moreover, the damping-control valve arrangement is preferably designed as a force-proportional valve, so that the damping force is essentially independent of the stroke speed of the piston or displacer.
A hydraulic shock absorber of the above-mentioned type is described in German Patent Document 3,835,705.
In such a shock absorber, it is advantageous that operability is ensured even in the event of a failure of the electromagnet arrangement. This is because there still remains a minimum damping force which is determined by the dimensioning of the spring arrangement.
Furthermore, it is known from German Patent Document 3,835,705, by means of the electromagnet arrangement, to control the closing force of a pilot control valve which then itself influences a damping-control valve. Large variations of the damping force can be achieved in this way with comparatively small electromagnet arrangements.
In a shock absorber known from German Utility Model 86 10 374, the closing member of a damping-control valve constitutes the armature of an electromagnet The electromagnet is designed such that the forces generated when current passes through the electromagnet seek to urge the closing member in the opening direction counter to the force of a spring arrangement. Here too, the shock absorber remains operational in the event of a failure of the electromagnet In such an instance, the damping behavior is simply determined solely by the characteristic of the spring arrangement.
German Patent Document 2,536,578 and EP-A-0,330,634 describe further controllable or regulatable hydraulic shock absorbers. In these shock absorbers, the orifice cross-section, opened by a damping-control valve in a line between the two working chambers, is likewise dependent on the pressure difference between the two working chambers. Here too, the proportionality factor between the orifice cross-section and the pressure difference is influenced by an electromagnet arrangement. At the same time, the electromagnet arrangement controls in each case a pilot control valve, the setting of which can then indirectly influence the above-mentioned proportionality factor
According to German Patent Document 2,536,578, the electromagnet drive of the pilot control valve is self-locking, such that, in the event of a failure of the electromagnet arrangement, the particular setting of the pilot control valve last selected is maintained.
According to EP-A-0,330,634, if the electromagnet arrangement fails the pilot control valve assumes one end position, in which the shock absorber has an especially week action.
In the above-described shock absorbers, if the electromagnet arrangement fails there is either an especially hard or an especially weak damping. Correspondingly, in emergency operation, that is to say in the event of a failure of the electromagnet arrangement, either marked loss of comfort because of especially hard damping or loss of safety because of especially weak damping have to be taken into account.
German Patent Document 3,635,894 makes known a further controllable or regulatable hydraulic shock absorber, in which there is an armature arrangement. The armature arrangement, depending on the direction in which current passes through the electromagnet arrangement, displaces a closing member in the closing direction or in the opening direction, so that the damping resistance either increases or decreases. The closing member is designed as a rotary slide, and therefore the pressure differences between the working chambers of the shock absorber exert no adjusting forces on the closing member. The respective orifice cross-section opened by the closing member between the working chambers of the shock absorber therefore depends solely on the intensity and direction of the electrical current passing through the electromagnet arrangement. A force-proportional opening behavior cannot be obtained in this way.
Furthermore, in the shock absorber of German Patent Document 3,635,894, when electrical current does not pass through the electromagnet arrangement the closing member is held by springs in a middle position, in which the closing member opens a medium orifice cross-section between the working chambers of the shock absorber.
There is therefore needed a shock absorber of the above-mentioned type which is distinguished by the best possible emergency running properties in the event of a failure of the electromagnet arrangement.
This need is met, according to the present invention, in that the armature arrangement can be loaded in the direction to strengthen and/or weaken the closing force of the closing member, depending on the passage of current through the electromagnet arrangement.
The present invention ensures, by an appropriate dimensioning of the spring arrangement urging the closing member into the closing position, a basic damping which remains effective in the event of a failure of the electromagnet arrangement and which is dimensioned as would be desirable or ideal in an arrangement of hydraulic shock absorbers which are not controllable or regulatable. Because a variation of the closing force both with the effect of a strengthening and with the effect of a weakening is now possible by means of the electromagnet arrangement, when the electromagnet arrangement works correctly the damping best suited to the particular operating circumstances can be achieved.
It is advantageous, furthermore, that the relative speed between the sprung mass or vehicle body and non-sprung mass or wheels need not be taken into account in the regulation of the damping force. This is because the parameter is at most of subsidiary importance as regards the operating behavior when the features indicated above are present.
According to a first preferred embodiment, there can be provision for the armature arrangement to interact with two magnet coils, the flow of current through one magnet coil bringing about a strengthening of the damping force and the flow of current through the other magnet coil bringing a weakening of the damping force.
It is also possible to design the armature arrangement as a permanent magnet, in which case a strengthening or a weakening of the damping force occurs, depending on the direction in which current flows through an associated magnet coil.
It is expedient, furthermore, to connect the damping-control valve arrangement to non-return valves, in such a way that both in the compression stage and in the extension stage of the shock absorber the exchange of hydraulic medium between the working chambers always takes place via the same damping-control valve and always passes through this in the same direction of flow.
The non-return valves, which can be designed in a basically known way as spring-plate valves, can be dimensioned differently, in such a way that the non-return valves opened in the compression stage have a different throttle resistance than the non-return valves opened in the extension stage. A different basic damping can thus be achieved for the compression stage and the extension stage.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings